In a concentric double axis mechanism in which each axis (i.e., an axis-A and another axis-B) is equipped with its corresponding actuator; the actuator for driving the axis-A, for example, needs to operate while having the actuator for driving the axis-B as a load for the axis-A. The actuator for driving the axis-A bears a greater load in comparison with the actuator for driving the axis-B. In the case of high speed driving in particular, the actuator of the axis-B as the load for the actuator of the axis-A causes a great disadvantage.